This invention was made in part with United States governmental support under Grant No. 0900542 awarded by the National Science Foundation. The U.S. government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATION

Not Applicable.

BACKGROUND

This invention is generally related to maximizing window efficiency and enabling control of the transmission of solar radiation into the interior of a building. This invention more specifically relates to advanced smart windows for high energy efficiency and recycling capability which include a diffraction grating for separation of different spectral regions for selective rejection and/or transmission of infrared, visible and ultraviolet radiation into the interior of a building.

This invention also relates to low-cost energy-efficient window technologies that incorporate a set of diffractive structures optimized to provide the desired objectives of a smart window. For example smart windows described herein are useful for lowering cooling costs in the summer season, lowering heating costs in the winter season, and lowering interior lighting costs throughout the year.

White light from the sun has a broad range of wavelengths. Among them, visible (VIS) rays with wavelengths ranging from about 0.4 μm to about 0.7 μm are always useful to humans, while infrared (IR) rays with wavelengths ranging from about 0.7 μm to about 3.0 μm are only useful for some seasons. Approximately 40% of total solar flux lies in the infrared spectral region and 40% in the visible, the remainder being distributed among wavelengths longer than 3 μm and shorter that 0.4 μm. In the summer season, it is frequently desired to reject the entry of solar heat into a building to reduce the building cooling costs, whereas in winter season it is desirable to permit the solar IR radiation to enter the building to reduce the heating costs. The function of conventional energy saving window technologies is currently confined to simply blocking the solar radiation (e.g., when the heat is not desired) without considering the wavelength of the incident light, so this leads to a need for extra interior lighting even in daylight hours.

From an optics perspective, conventional windows are classified as passive devices that function depending upon inherent characteristics of the glass and polymeric materials of which they are constructed. With conventional windows, mechanical methods are generally used to physically block direct solar radiation. Typical examples include awnings, louvers, blinds, etc. which usually have a fixed construction but can be made adjustable or retractable in response to changes in solar radiation direction. Louvers and blinds are typically composed of slats varying in size, width, and shape depending on the application. They are mainly intended for shading, but can also be used to redirect daylight, reduce glare, and control solar heat gain. Fixed mechanical systems are usually available at a low cost, but controllable mechanical systems can be more expensive. A major drawback is that mechanical methods typically block daylight when only heat-blocking is desired.

Passive optical methods have also been utilized for redirecting daylight, reducing glare, and controlling solar heat gain. Spectrally selective coatings applied to window glass typically reject a specific fraction of the solar spectrum, generally ultraviolet and infrared radiation, while admitting visible radiation. In this way, such a coating can allow visible light to be transmitted through a window, but blocks heat-generating ultraviolet and/or infrared radiation. Spectrally selective coatings are typically composed of thin metal films or a dielectric-metal multilayer stack which is coated or applied to the glass window. Such coatings can reduce solar heat gain, and thus directly benefit buildings situated in hot climates where the cooling load is a major energy cost. They can also be applied inside of a building to reduce heat loss through the windows in cold climates but will also block incoming heat from direct daylight, which is an important natural heating source. This technology, however, is not ideal for use in mixed climates because the coating property is fixed once it has been applied to the window.

A smart window, however, can be an active device which can control optical transmittance, for example by application of a set of electric signals. Various active window systems exist, all of which have major limitations. For example, one technical approach for smart windows is mainly limited to changing only one optical property, transmittance, for all ranges of wavelengths.

A photochromic window is one example of such a smart window. Photochromic windows experience a photochemical reaction under exposure to solar radiation in a specific spectral range, usually UV. This reaction changes the optical absorption band of the window, which is originally transparent to visible radiation, resulting in a change of color. The reaction can be reversed by eliminating the light source that has activated the transformation. The optical transparency is automatically varied with the intensity of the incident light. Such a window has the weakness that it can work only depending on the intensity of the external light, thereby not meeting seasonal requirements; for example, in summer months it blocks infrared radiation as well as useful visible light. Photochromic technology is widely known for its use in sunglass lenses.

Similarly, thermotropic or thermochromic windows change their optical properties in response to a temperature change. In general, they are transparent at lower temperatures and become translucent or opaque at higher temperatures. The basic mechanism is based on the movement of the component molecules to cause a phase change in the material, which scatter light accordingly. The major commercial applications of these materials are skylights and upper windows where visual comfort can be ignored.

Photochromic, thermotropic, and thermochromic windows are self-regulating, which make them less useful as energy saving devices since they can not be manually controlled to respond to the changing environment. Their optical properties can change when exposed to UV radiation and/or altered temperature. Photochromic materials will block heat on a sunny cold winter day, and thermotropic materials will block visible light on a warm summer day.

Active materials, such as those used in liquid crystal displays have an advantage over the use of photochromic and thermochromic materials in smart windows since they are electrically programmable and switchable. Commercially available liquid crystal displays are typically composed of two polarized glass substrates with a liquid crystal region between them and have transparent oxide electrodes. The first glass substrate is polarized in one direction and the second one is polarized in a perpendicular direction. In the off state, the liquid crystal molecules rotate the polarization of the light by 90 degrees, allowing incident light to pass through the two glass substrates without optical loss. When an electric field is applied, the liquid crystals will align and no longer rotate the polarization of the incident light; thus, the display will be opaque.

A polymer dispersed liquid crystal (PDLC) material is another useful liquid crystal system; however, the liquid crystal structure used in PDLC smart windows is somewhat different from that of a liquid crystal display. In a PDLC smart window, an emulsion of a polymer and liquid crystal is formed into a film. The refractive index of the polymer matrix is matched to the dispersed liquid crystal. The film is then sandwiched between two transparent sheets which are coated with a transparent conducting material, such as Indium Tin Oxide (ITO). In the off state, randomly oriented liquid crystals scatter light, making the film translucent. When an electric field is applied, the dispersed liquid crystals align parallel to the field and change the film's transparency. These windows are suitable for privacy windows, as they do not sacrifice light; however, they cannot efficiently block heat. The lack of a memory effect requires continuous power to hold the window in a transparent state; therefore, the power consumption is ultimately higher than that of other materials which only require power during switching.

Suspended particle system (SPS) windows utilize a similar concept as PDLC windows except that they use light absorbing microparticles instead of scattering liquid crystals to make the window opaque. SPS windows have an active polymer layer where the light absorbing microparticles are suspended. This layer is sandwiched between two sheets coated with transparent conductors, for example ITO, with a dielectric layer on top. In the off state, the suspended particles are randomly distributed and absorb light, making the film opaque. By applying an electric field to the active layer through the transparent conductors, the particles align to the field and change the transparency of the film. An application similar to SPS is electrophoretic electronic paper, also know as E-ink, which utilizes the migration of color coated suspended particles under the influence of an applied electric field. Since heat and light are both absorbed, the major application of SPS windows is shading, and illumination may be required inside a building, increasing energy use.

Electrochromic windows are among the most technologically advanced window systems. Instead of using suspended particles or liquid crystals, electrochromic materials are typically composed of a stack of an electrochromic layer, a conducting electrolyte layer, and an ion storage layer, all of which are placed between transparent conductors, such as ITO. They are transparent in the off state, and optical properties of the electrochromic layer can be changed by the injection of coloration ions from the storage layer. An applied electric field drives ions from the storage layer through the conducting layer to the electrochromic layer, altering the electronic structure of the electrochromic layer. This reaction switches the window from the transparent state to the opaque state. A reverse electric field will draw the coloration ions back into the storage layer switching the electrochromic layer back to its original clear state. Various coloration ions such as Li+, H+, Na+, and Ag+ can be utilized. Inorganic oxides such as WO3, NiO, V2O5, and MoO3 can be used for the electrochromic layer, among which WO3 has been most widely studied. Electrochromic windows only consume power during switching, require a low driving voltage (1-5V) and have long term memory (12-48 h), making this technology energy efficient. However, fabrication of large area windows is very expensive (˜$50-100/ft2) and illumination is still required since the window absorbs or reflects the visible light.

Gasochromic materials share the principle of electrochromic materials except that the coloration ions are supplied by means of gas. Hydrogen (H2) gas is typically injected between two panes, where one of the panes has a coating of a thin catalytic layer on top of a chromogenic layer, for example WO3. Decoloration can be achieved by feeding another purging gas. The major drawback with this technique is the need of integration of gas lines into the window which is a large construction limitation.

U.S. Pat. No. 6,094,306 describes an energy-efficient window concept that utilizes multiple diffraction gratings that can be arranged in different ways to enable different cumulative angular deviations of the transmitted radiation. Although this technique is effective in providing angular discrimination between different configurations, it does not satisfactorily address the higher-order diffraction effects that result in wavelength mixing. U.S. Patent Application Publication No. US 2009/0296188 and U.S. Pat. No. 7,940,457, hereby incorporated by reference in their entireties, describe a smart window technology that utilizes a two-dimensional pixelated array of electro-optic active devices. While highly versatile in controllability, this technology also requires extensive and expensive microelectronic fabrication processes.

SUMMARY

Energy-efficient windows incorporating spectrally selective optical elements capable of providing desirable optical characteristics (transmission, reflection, refraction or diffraction) for different wavelengths are disclosed herein. More specifically, energy-efficient windows incorporating suitably designed diffraction gratings to optimize the efficiency of the utilization of different spectral components of the solar radiation are disclosed.

In one aspect, provided herein are smart windows. An embodiment of this aspect comprises a first blazed diffraction grating for diffracting visible electromagnetic radiation, the first blazed diffraction grating having a first blaze direction, a first grating pitch and a first blaze angle; and a second blazed diffraction grating for diffracting near-infrared electromagnetic radiation, the second blazed diffraction grating having a second blaze direction, a second grating pitch and a second blaze angle and positioned in optical communication with the first blazed diffraction grating for receiving electromagnetic radiation at least partially diffracted by the first blazed diffraction grating; and wherein the first grating pitch and the second grating pitch are different, wherein the first blaze angle and the second blaze angle are different and wherein the first blaze direction is oriented opposite to the second blaze direction.

In embodiments, the first grating pitch is smaller than the second grating pitch. Optionally, the first grating pitch is selected over the range of 1 μm to 3 μm. Optionally, the second grating pitch is selected over the range of 2 μm to 6 μm. In embodiments, the first blaze angle is smaller than the second blaze angle. Optionally, the first blaze angle is selected over the range of 20 to 35 degrees. Optionally, the second blaze angle is selected over the range of 25 to 40 degrees. In a specific embodiment, the first grating pitch and the first blaze angle provide for diffraction of visible electromagnetic radiation by the first diffraction grating. In an embodiment, the second grating pitch and the second blaze direction provide for diffraction of near-infrared electromagnetic radiation by the second diffraction grating.

In embodiments, a smart window further comprises a retroreflector positioned in optical communication with the second blazed diffraction grating for receiving electromagnetic radiation at least partially diffracted by the first blazed diffraction grating and/or at least partially diffracted by the second blazed diffraction grating. For example, in an embodiment, the retroreflector reflects near-infrared electromagnetic radiation, such as near-infrared electromagnetic radiation diffracted by the second blazed diffraction grating. In embodiments, a retroreflector occupies a large area, for example, an area of greater than 1 ft2. Optionally, a retroreflector is formed using an embossing method. For example, U.S. Pat. No. 6,644,818 discloses an embossing roll and techniques for forming embossed retroreflective structures.

Useful blazed diffraction gratings include dynamically controllable diffraction gratings, electrically controllable diffraction gratings, fixed diffraction gratings, physical diffraction gratings, phase diffraction gratings and permanent diffraction gratings. In embodiments, a blazed diffraction grating occupies a large area, for example, an area greater than 1 ft2. In an embodiment, a large-area blazed diffraction grating is formed from using a lithographic patterning technique. In embodiments, a large-area blazed diffraction grating is formed from an array of smaller blazed diffraction gratings. For example, multiple blazed diffraction gratings made using a ruling engine or a lithographic patterning technique can be placed adjacent to one another to form a large-area blazed diffraction grating. Optionally, a large-area blazed diffraction grating is formed using an embossing method. In one embodiment, a patterned cylindrical embossing roll is used for embossing a blazed diffraction grating. Useful embossing rolls include those patterned by a ruling engine or a lithographic patterning technique. Useful embossing rolls include those molded from a patterned master, for example a master mold patterned by a ruling engine or a lithographic patterning technique.

In a specific embodiment, a smart window further comprises a first window pane. Optionally, the first blazed diffraction grating is incorporated into the first window pane. Optionally, the first blazed diffraction grating comprises a film on the first window pane. In embodiments, the second blazed diffraction grating is incorporated into the first window pane or comprises a film on the first window pane.

In a specific embodiment, a smart window further comprises a first window pane and a second window pane positioned in optical communication with the first window pane. Optionally, the second blazed diffraction grating is incorporated into the second window pane. Optionally, the second blazed diffraction grating comprises a film on the second window pane. In specific embodiments, a space is provided between a first window pane and a second window pane. Useful window pane spacings include those selected over the range of 0 to 5 cm.

In embodiments, a smart window further comprises one or more additional blazed diffraction gratings, for example a third blazed diffraction grating, a fourth blazed diffraction gratings, etc. In an embodiment, an additional blazed diffraction grating is useful for diffracting near-infrared electromagnetic radiation or visible electromagnetic radiation. In general, each additional blazed diffraction grating has its own blaze direction, its own grating pitch and its own blaze angle, and is positioned in optical communication with one or more other blazed diffraction gratings in a smart window, for example for receiving at least partially diffracted electromagnetic radiation from another blazed diffraction grating and/or for providing at least partially diffracted electromagnetic radiation to another blazed diffraction grating. In a specific embodiment, a first blazed diffraction grating is optimized for diffraction of visible electromagnetic radiation and a second blazed diffraction grating and a third blazed diffraction grating are optimized for diffraction of different spectral regions of near-infrared electromagnetic radiation.

Optionally, the grating pitches of each blazed diffraction grating in a smart window are independent. In a specific embodiment, the grating pitches of the different blazed diffraction gratings are different. Optionally the blaze angles of the different blazed diffraction gratings in a smart window are independent. In a specific embodiment, the blaze angles of the different blazed diffraction gratings are different.

Optionally, the blaze directions of the different blazed diffraction gratings in a smart window are independent. In a specific embodiment, however, the blaze direction for each visible blazed diffraction grating is oriented opposite to the blaze direction of each near-infrared blazed diffraction grating. For example, in an embodiment, the blaze directions for all visible blazed diffraction gratings in a smart window are the same and the blaze directions for all near-infrared blazed diffraction gratings in a smart window are the same but oriented opposite to the blaze directions for the visible blazed diffraction gratings.

In a specific embodiment, two or more blazed diffraction gratings in a smart window are parallel. In certain embodiments, two or more blazed diffraction gratings in a smart window are not exactly parallel. In specific embodiments, two or more blazed diffraction gratings in a smart window are substantially parallel, for example, where the gratings in any pair of blazed diffraction gratings are relatively oriented within 5 degrees from being exactly parallel to each other.

In embodiments, the blaze directions of two or more blazed diffraction gratings in a smart window are opposite. In embodiments, the blaze directions of two or more blazed diffraction gratings in a smart window are the same. For certain embodiments, the blaze directions of two or more blazed gratings are oriented substantially opposite, for example where the blaze directions of the gratings in any pair of blazed diffraction gratings are relatively oriented within 5 degrees from exactly opposite. For certain embodiments, the blaze directions of two or more blazed gratings are oriented to be substantially the same, for example, where the blaze directions of the gratings in any pair of blazed diffraction gratings are relatively oriented within 5 degrees from being exactly the same.

Useful grating pitches for a blazed diffraction grating include those selected over the range of 1.0 μm to 6.0 μm. In a specific embodiment, the grating pitch is selected over the range of 1 μm to 3 μm. In a specific embodiment, the grating pitch is selected over the range of 2 μm to 6 μm. Optionally, the grating pitch is smaller than 2.5 μm. Optionally, the grating pitch is larger than 2.5 μm.

Useful blaze angles for a blazed diffraction grating include those selected over the range of 10 to 50 degrees. In specific embodiments, the blaze angle is selected over the range of 20 to 35 degrees. In specific embodiments, the blaze angle is selected over the range of 25 to 40 degrees. Optionally, the blaze angle is smaller than 30 degrees. Optionally, the blaze angle is larger than 30 degrees.

In specific embodiments, a smart window comprises a first blazed diffraction grating for diffracting visible electromagnetic radiation, the first blazed diffraction grating having a first blaze direction, a first grating pitch and a first blaze angle and positioned for receiving electromagnetic radiation; a second blazed diffraction grating for diffracting near-infrared electromagnetic radiation of a certain spectral region, the second blazed diffraction grating having a second blaze direction, a second grating pitch and a second blaze angle and positioned in optical communication with the first blazed diffraction grating for receiving electromagnetic radiation at least partially diffracted by the first blazed diffraction grating; and a third blazed diffraction grating for diffracting near-infrared electromagnetic radiation of a different spectral region than that in the case of the second blazed diffraction grating, the third blazed diffraction grating having a third blaze direction, a third grating pitch and a third blaze angle and positioned in optical communication with the second blazed diffraction grating for receiving electromagnetic radiation at least partially diffracted by said second blazed diffraction grating.

In an embodiment, the first grating pitch and the second grating pitch are different. In an embodiment, the first blaze angle and the second blaze angle are different. In an embodiment the first blaze direction is oriented opposite to the second blaze direction. In an embodiment, the first grating pitch and the third grating pitch are different. In an embodiment, the first blaze angle and the third blaze angle are different. In an embodiment, the first blaze direction is oriented opposite to the third blaze direction.

A specific embodiment further comprises a fourth blazed diffraction grating for diffracting near-infrared electromagnetic radiation of a spectral region different from those in the cases of the second and third blazed diffraction gratings, the fourth blazed diffraction grating having a fourth blaze direction, a fourth grating pitch and a fourth blaze angle, and positioned in optical communication with the third blazed diffraction grating for receiving at least partially diffracted electromagnetic radiation. In an embodiment, the first grating pitch and the fourth grating pitch are different. In an embodiment, the first blaze angle and the fourth blaze angle are different. In an embodiment, the first blaze direction is oriented opposite to the fourth blaze direction.

In an specific embodiment, a smart window comprises a first blazed diffraction grating for diffracting visible electromagnetic radiation, the first blazed diffraction grating having a first blaze direction, a first grating pitch and a first blaze angle; and a second blazed diffraction grating for diffracting near-infrared electromagnetic radiation, the second blazed diffraction grating having a second blaze direction, a second grating pitch and a second blaze angle and positioned in optical communication with the first blazed diffraction grating for receiving electromagnetic radiation at least partially diffracted by the first blazed diffraction grating, wherein the first blaze direction is oriented opposite to said second blaze direction; and wherein the first grating pitch is selected over the range of 1 μm to 3 μm and the first blaze angle is selected over the range of 20 to 35 degrees, thereby providing for diffraction of visible electromagnetic radiation by the first diffraction grating; and wherein the second grating pitch is selected over the range of 2 μm to 6 μm and the second blaze direction is selected over the range of 25 to 40 degrees, thereby providing for diffraction of near-infrared electromagnetic radiation by the second diffraction grating.

In a specific smart window embodiment, a blazed grating is positioned for receiving incident solar electromagnetic radiation. In an embodiment, the smart window is an external window on a building, such that an external surface of the smart window is exposed to incident solar radiation and the opposite external surface of the smart window faces the interior of the building. In an embodiment, the smart window is a window on a commercial building. In an embodiment, the smart window is a window on a residential building. In an exemplary embodiment, the smart window is a south facing window.

Optionally, smart window embodiments further comprise a UV blocking layer, for example positioned in optical communication with a window pane and/or a diffraction grating. In an embodiment, a UV blocking layer comprises a UV absorbing film, for example applied or deposited on a surface of a window pane. In certain embodiments, a window pane comprises a UV blocking layer, for example a window pane comprising a UV absorbing polymer or a window pane comprising UV absorbing particles. In certain embodiments, a UV blocking layer comprises a reflective dielectric multilayer, for example a reflective dielectric multilayer applied or deposited on a surface of a window pane.

In another aspect, provided are methods for spatially separating visible and near infrared electromagnetic radiation. One method of this aspect comprises the steps of providing a smart window as described herein and passing solar electromagnetic radiation through the smart window, thereby spatially separating solar visible and solar near infrared electromagnetic radiation. A specific method of this aspect comprises the steps of providing a first blazed diffraction grating, the first blazed diffraction grating having a first blaze direction, a first grating pitch and a first blaze angle; providing a second blazed diffraction grating positioned in optical communication with the first blazed diffraction grating, the second blazed diffraction grating having a second blaze direction, a second grating pitch and a second blaze angle, and wherein the first grating pitch and the second grating pitch are different, wherein the first blaze angle and the second blaze angle are different and wherein the second blaze direction is oriented opposite to said first blaze direction; passing visible electromagnetic radiation and near-infrared electromagnetic radiation through the first blazed diffraction grating, wherein at least a portion of the visible electromagnetic radiation is diffracted by the first blazed diffraction grating in a first diffraction direction and a majority of said near-infrared electromagnetic radiation is not diffracted by said first blazed diffraction grating, thereby generating diffracted visible electromagnetic radiation and non-diffracted near-infrared electromagnetic radiation; passing the diffracted visible electromagnetic radiation and the non-diffracted near-infrared electromagnetic radiation through the second blazed diffraction grating, wherein at least a portion of the non-diffracted near-infrared electromagnetic radiation is diffracted by the second blazed diffraction grating in a second diffraction direction, thereby generating diffracted near-infrared electromagnetic radiation; wherein the first diffraction direction is different from the second diffraction direction, thereby spatially separating said visible electromagnetic radiation and said near-infrared electromagnetic radiation. In a specific embodiment, the first grating pitch is smaller than the second grating pitch. In a specific embodiment, the first blaze angle is smaller than the second blaze angle.

Another method of this aspect comprises the steps of providing a first blazed diffraction grating, the first blazed diffraction grating having a first blaze direction, a first grating pitch and a first blaze angle; providing a second blazed diffraction grating positioned in optical communication with the first blazed diffraction grating, the second blazed diffraction grating having a second blaze direction, a second grating pitch and a second blaze angle, wherein the first grating pitch and the second grating pitch are different, wherein the first blaze angle and the second blaze angle are different and wherein the second blaze direction is oriented opposite to the first blaze direction; providing a third blazed diffraction grating positioned in optical communication with the second blazed diffraction grating, the third blazed diffraction grating having a third blaze direction, a third grating pitch and a third blaze angle, wherein the first grating pitch and the third grating pitch are different, wherein the first blaze angle and the third blaze angle are different and wherein the third blaze direction is oriented opposite to the first blaze direction; passing visible electromagnetic radiation and near-infrared electromagnetic radiation through the first blazed diffraction grating, wherein at least a portion of the visible electromagnetic radiation is diffracted by the first blazed diffraction grating in a first diffraction direction and a majority of the near-infrared electromagnetic radiation is not diffracted by the first blazed diffraction grating, thereby generating diffracted visible electromagnetic radiation and non-diffracted near-infrared electromagnetic radiation of a first wavelength or wavelength region; passing the diffracted visible electromagnetic radiation and the non-diffracted near-infrared electromagnetic radiation of the first wavelength or wavelength region through the second blazed diffraction grating, wherein at least a portion of the non-diffracted near-infrared electromagnetic radiation of the first wavelength or wavelength region is diffracted by the second blazed diffraction grating in a second diffraction direction, thereby generating diffracted near-infrared electromagnetic radiation of a second wavelength or wavelength region and non-diffracted near-infrared electromagnetic radiation of a third wavelength or wavelength region; and passing the diffracted visible electromagnetic radiation, the diffracted near-infrared electromagnetic radiation of the second wavelength or wavelength region and the non-diffracted near-infrared electromagnetic radiation of the third wavelength or wavelength region through the third blazed diffraction grating, wherein at least a portion of the non-diffracted near-infrared electromagnetic radiation of the third wavelength or wavelength region is diffracted by the third blazed diffraction grating in a third diffraction direction, thereby generating diffracted near-infrared electromagnetic radiation of a fourth wavelength or wavelength region; wherein the first diffraction direction is different from the second diffraction direction, the third diffraction direction or both the second diffraction direction and the third diffraction direction, thereby spatially separating the visible electromagnetic radiation and the near-infrared electromagnetic radiation.

In one embodiment, the first, second and third diffraction directions are different. In another embodiment the second diffraction direction is the same as the third diffraction direction. In an embodiment, the first grating pitch is smaller than the second grating pitch and the third grating pitch. In an embodiment, the first blaze angle is smaller than the second blaze angle and the third blaze angle. In an embodiment, the first wavelength or wavelength region is different from the fourth wavelength or wavelength region.

In embodiments, methods of this aspect further comprise the steps of providing a retroreflector in optical communication with the second blazed diffraction grating; and reflecting at least a portion of the diffracted near-infrared electromagnetic radiation with the retroreflector.

In another aspect, provided are methods of dynamically controlling the transmission and/or rejection of solar near-infrared electromagnetic radiation. A method of this aspect comprises the steps of providing a smart window as described herein, passing solar electromagnetic radiation through the smart window, thereby generating diffracted near-infrared electromagnetic radiation, and dynamically controlling the presence or absence of a retroreflector positioned to retroreflect the diffracted near-infrared electromagnetic radiation. Another method of this aspect comprises the steps of providing a smart window as described herein, passing solar electromagnetic radiation through the smart window, thereby generating diffracted near-infrared electromagnetic radiation, and dynamically controlling the orientation of a retroreflector positioned to selectively retroreflect the diffracted near-infrared electromagnetic radiation.

Without wishing to be bound by any particular theory, there can be discussion herein of beliefs or understandings of underlying principles relating to the invention. It is recognized that regardless of the ultimate correctness of any mechanistic explanation or hypothesis, an embodiment of the invention can nonetheless be operative and useful. It will be evident to one having skill in the art that the accompanying drawings may not be to scale to better illustrate certain aspects of the invention.

FIG. 5B provides a schematic diagram showing diffraction of visible and near-infrared radiation by a first blazed diffraction grating optimized for diffraction of visible radiation and a second blazed diffraction grating optimized for diffraction of near-infrared radiation.

FIG. 6 provides a schematic diagram showing diffraction of visible and near infrared radiation by two blazed diffraction gratings and retroreflection of near-infrared radiation by a retroreflector.

FIG. 7 provides a schematic diagram showing the relationship between the angle of incidence, azimuth and elevation angles of solar radiation.

DETAILED DESCRIPTION

In general the terms and phrases used herein have their art-recognized meanings, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of the invention.

“Diffraction” refers to the optical interference phenomenon arising from the interaction between electromagnetic radiation and a physical object. As used herein, use of the term diffraction is intended to be consistent with use in the field of optics.

“Diffraction grating” refers to a repetitive array of diffracting elements having the effect of producing periodic alterations in the phase, amplitude or both of incident electromagnetic radiation. In embodiments, a diffraction grating comprises an array of linear grooves. In embodiments, a diffraction grating comprises an array of linear slits. In embodiments, a diffraction grating comprises a repetitive array of different indices of refraction. In embodiments, a diffraction grating is planar or substantially planar. In embodiments, a diffraction grating is non-planar.

A “controllable diffraction grating” refers to a diffraction grating having a diffractive structure which is dynamically controllable, for example by application of an electric voltage and/or current. In contrast, a “fixed diffraction grating” or a “permanent diffraction grating” refers to a diffraction grating having a non-dynamic diffractive structure. In an embodiment, a fixed diffraction grating comprises a repetitive array of physical diffractive structures. In an embodiment a controllable diffraction grating comprises a material with controllable optical properties, such as index of refraction. Controllable diffraction gratings are described in U.S. Pat. No. 7,940,457 which is hereby incorporated by reference.

“Grating pitch” refers to the spatial separation between repetitive elements in a diffraction grating. FIG. 1A illustrates an embodiment of a diffraction grating 100 with grating pitch 130.

A “blazed grating” or “blazed diffraction grating” is a special type of diffraction grating that allows the diffracted radiation in a given spectral region to be highly concentrated into a desired, specific, non-zero diffraction order (generally +1 or −1). In embodiments, this is accomplished by forming grooves of a properly designed saw-tooth profile, as illustrated in FIG. 1A. Such grooves, for example, can comprise physical material and/or a spatial arrangement of indices of refraction. In embodiments, the specific inclination of the groove face provides a constructive phase relationship between electromagnetic radiation exiting from different grooves, thus enabling the diffracted light of the given spectral band to be concentrated into a desired single diffraction order. In embodiments, this configuration allows a blazed grating to separate different wavelengths of electromagnetic radiation extremely efficiently.

“Blaze angle” refers to the specific inclination of the groove face of a blazed grating. FIG. 1A illustrates an embodiment of a blazed diffraction grating 100 having blaze angle 110.

In an embodiment, a blazed grating which “provides for diffraction” or is “optimized for diffraction” or is “for diffraction” or is “blazed for diffraction” of a specific wavelength or wavelength region of electromagnetic radiation has a grating pitch and blaze angle selected such that the blazed grating concentrates diffracted electromagnetic radiation of the specific wavelength or wavelength region into a desired non-zero diffraction order (e.g., +1 or −1). In embodiments, wavelengths or wavelength regions falling outside of the specific wavelength region that the blazed grating is optimized for remain undiffracted or may be at least partly diffracted into a non-desired diffraction order.

“Diffraction direction” refers to a relative angular deviation between radiation incident on a diffraction grating or series of diffraction gratings and radiation diffracted by the diffraction grating or series of diffraction gratings.

“Blaze direction” refers to a relative direction of a blazed diffraction grating indicating the direction, relative to the incident radiation, that the concentrated diffraction mode occurs. FIG. 1A illustrates an embodiment of a blazed diffraction grating 100 and indicates the blaze direction 120. In embodiments, blaze directions that are “oriented opposite” to one another refers to the relative orientation between two diffraction gratings such that their blaze directions are generally oriented 180° from one another. FIG. 1B illustrates two blazed diffraction grating embodiments 101 and 102 and indicates the blaze directions 121 and 122 are oriented opposite. In embodiments, blaze directions that are “substantially opposite” to one another refers to the relative orientation between two diffraction gratings such that their blaze directions are generally oriented at an angle of more than 170° from one another.

“Visible electromagnetic radiation” generally refers to electromagnetic radiation that can be detected by the human eye. In embodiments, visible electromagnetic radiation has a wavelength selected between about 400 nm and about 700 nm.

“Infrared electromagnetic radiation” generally refers to electromagnetic radiation having wavelengths longer than visible electromagnetic radiation, for example having a wavelength selected between about 700 nm and about 10000 nm. “Near-infrared electromagnetic radiation” refers to that portion of infrared electromagnetic radiation having wavelengths closest to visible electromagnetic radiation, for example between about 700 nm and about 3000 nm.

“Retroreflector” refers to a reflective element used for reflecting incident radiation back towards its source. In embodiments, a retroreflector comprises a mirrored surface. In embodiments, a retroreflector comprises a corner cube element. In embodiments, a retroreflector comprises an array of corner cube elements. In embodiments, a retroreflector comprises an array of cat\'s eye type elements.

A “pane” refers to a sheet of material used in a window, for example a sheet of material which is at least partially transparent to visible electromagnetic radiation. In an embodiment, a pane is a large-area sheet, for example having an area greater than 1 ft2. In embodiments, a window pane comprises a glass. In embodiments, a window pane comprises a polymer, for example a plastic or a thermoplastic.

“Film” refers to a coating or layer of material positioned on a substrate such as a window pane. In an embodiment, a film includes a patterned structure, such as a diffraction grating or a retroreflector. In an embodiment, a film is deposited directly on a substrate. In an embodiment, a film is applied to a substrate, for example, as a continuous layer of material from a roll. In embodiments, films are patterned using a lithographic method. In embodiments, films are patterned using a stamping or molding process. In embodiments, films are patterned using an embossing roll.

“Optical communication” refers to a configuration of two or more elements wherein one or more beams or rays of electromagnetic radiation are capable of propagating from one element to the other element. Elements in optical communication may be in direct optical communication or indirect optical communication. “Direct optical communication” refers to a configuration of two or more elements wherein one or more beams or rays of electromagnetic radiation propagate directly from a first element to another without use of optical components for steering and/or combining the beams or rays. “Indirect optical communication” refers to a configuration of two or more elements wherein one or more beams or rays of electromagnetic radiation propagate between two elements via one or more device components including, but not limited to, waveguides, fiber optic elements, windows, reflectors, filters, prisms, lenses, gratings and any combination of these.

FIG. 1A illustrates a blazed diffraction grating embodiment. Grating 100 has a blaze angle 110 and grating pitch 130. In this embodiment, blaze angle 110 is approximately 21 degrees. FIG. 1A also indicates the blaze direction 120 of grating 100. FIG. 1B illustrates two blazed diffraction grating embodiments. Grating 101 has a blaze angle 111 and grating pitch 131. Grating 102 has a blaze angle 112 and grating pitch 132. In this embodiment, blaze angle 111 is approximately 25 degrees and blaze angle 112 is approximately 35 degrees. In this embodiment, grating pitch 131 is approximately one-half of grating pitch 132. Blaze directions 121 and 122 are indicated for grating 101 and 102, respectively, and are oriented opposite to one another.

FIG. 2A illustrates a smart window embodiment comprising first window pane 210, a first blazed grating 230, a second window pane 220 and a second blazed grating 240. First blazed grating 230 is shown as a film on first window pane 210 and second blazed grating 240 is shown as a film on second window pane 220. In this embodiment, blaze directions of first blazed grating 230 and second blazed grating 240 are opposite to one another. FIG. 2A shows an optional space between first blazed grating 230 and second blazed grating 240. Optionally, a smart window embodiment further includes a retroreflector (not shown in FIG. 2A), for example, for rejection of near-infrared electromagnetic radiation. Optionally, alternate configurations where first and second blazed gratings are films applied on a single window pane or where first and/or second blazed gratings are films applied on the exterior surface(s) of a double-pane window are contemplated. In an embodiment where solar radiation is first incident on first window pane 210, first blazed grating 230 comprises a blazed grating optimized for diffraction of visible electromagnetic radiation; in this embodiment, second blazed grating 240 comprises a blazed grating optimized for diffraction of near-infrared radiation.

FIG. 2B illustrates another smart window embodiment, comprising first window pane 211, first blazed grating 231, second blazed grating 241, second window pane 221 and third blazed grating 251. First blazed grating 231, second blazed grating 241 and third blazed grating 251 are shown as films. Optionally, a space is provided between first window pane 211 and second blazed grating 241 or between second blazed grating 241 and second window pane 221 (space not shown). In an embodiment, first blazed grating 231 is optimized for diffraction of visible electromagnetic radiation, second blazed grating 241 is optimized for diffraction of near-infrared electromagnetic radiation and third blazed grating 251 is optimized for diffraction of near-infrared electromagnetic radiation. In an embodiment, second blazed grating 241 is optimized for diffraction of near-infrared radiation of a different wavelength or wavelength region from that of third blazed grating 251. In an embodiment, first blazed grating 231 has a blaze direction that is opposite to the blaze directions of second blazed grating 241 and third blazed grating 251.

FIG. 2C illustrates another smart window embodiment, comprising first window pane 212 and second window pane 222. In this embodiment, first blazed diffraction grating 232 is incorporated into first window pane 212. Here, first window pane 212 comprises two layers 212A and 212B which together form first blazed diffraction grating 232, for example optimized for diffraction of visible radiation. In this embodiment, second blazed diffraction grating 242 is incorporated into second window pane 222. Here, second window pane 222 comprises two layers 222A and 222B which together form second blazed diffraction grating 242, for example optimized for diffraction of near-infrared radiation. In this embodiment, the two layers 212A and 212B of first window pane 212 comprise different materials; similarly, the two layers 222A and 222B of second window pane 222 comprise different materials. Optionally, a UV blocking layer (not shown) is provided on the external side of first window pane 212. Optionally, additional blazed diffraction gratings (not shown) are included for further facilitating the separation of portions of the electromagnetic spectrum. For example, an additional blazed diffraction grating for diffraction of visible radiation can be incorporated into a smart window. Additionally, or alternatively, for example, an additional blazed diffraction grating for diffraction of near-infrared radiation can be incorporated into a smart window.

The invention may be further understood by the following non-limiting examples.

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